Constant Current Stripping Chronopotentiometry Research Articles

Determination of Lead(II) by Constant Current Stripping Chronopotentiometry Using Bismuth Film Electrode after Extraction of the Bromide Complex into Propylene Carbonate

AbstractA selective and simple method is presented for the determination of Pb(II) by constant current stripping chronopotentiometric analysis (CCSCP) using bismuth film electrode. This method is based on the extraction of the bromide complex into propylene carbonate, followed by CCSCP measurements in the organic phase. CCSCP studies revealed that Pb(II) gave a characteristic response at about −0.52 V vs. Ag/AgCl on the stripping chronopotentiogram (dt/dE curve) after recording a potential vs. time curve at 3.0 μA. The peak height of Pb(II) response was directly proportional to the initial metal concentration of the aqueous phase in the ranges of 1.0–22.0 μg dm−3 (correlation coefficient 0.997) when the optimized parameters were used. A detection limit (S/N=3) of 0.0880 μg dm−3 Pb(II) was obtained at 180 s deposition time. The relative standard deviation was 3.2% on replicate runs (n=12) for the determination of 10.0 μg dm−3 Pb(II). Analysis of certified reference materials has confirmed the applicability of the proposed method for determination of Pb(II) in soil and water samples.

Bismuth Film Electrode in Metal Complexation Studies: Stripping Analysis of the Pb(II)‐, Cd(II)‐, and Zn(II)‐Binding with Phthalate

AbstractThe possibilities of bismuth film electrode for complexation studies by anodic stripping voltammetry (ASV) and constant current stripping chronopotentiometry (CCSCP) are tested for Pb(II), Cd(II), and Zn(II) in the presence of phthalate. In all cases, labile complexes are detected. The regular signals obtained for the Pb(II)‐phthalate system allow an accurate determination of stability constants by means of the DeFord‐Hume method. As for Cd(II)‐ions, the two overlapping signals usually present in the absence of ligands suffer a similar evolution with the addition of phthalate. Then, the use of an intermediate potential between both signals allows a reasonable estimation of stability constants. In contrast, the two overlapping signals obtained for Zn(II) behave in a quite irregular way in the presence of phthalate, thus hindering any quantitative analysis of the formed complexes.

Signal splitting in the stripping analysis of heavy metals using bismuth film electrodes: Influence of concentration range and deposition parameters

The stripping signals of Pb(II), Cd(II) and Zn(II) in a bismuth film electrode (BiFE) ex situ plated on glassy carbon support were studied by differential pulse anodic stripping voltammetry and constant-current stripping chronopotentiometry. Regular signals were measured for Pb(II), with a good linearity inside a wide concentration range. In contrast, Cd(II) and Zn(II) produce two overlapping signals, one predominating at low metal concentrations and the other at high metal concentrations. For the detailed study of such peak splitting, multivariate curve resolution by alternating least squares has been used concluding that the total area becomes linear with metal concentration in both situations. The reasons of the peak splitting seem to be related to the accumulation of the reduced metal on BiFE in different ways. Even with that complication, the fact that the linear relationship total area versus concentration is hold reinforces the applicability of BiFE for the determination of total concentrations of metal ions inside a wider concentration range than that initially expected. However, the coexistence of signals at different characteristic potentials anticipates important difficulties in the analysis of potential shifts caused by heavy metal complexation.

Adsorptive accumulation in constant current stripping chronopotentiometry as an alternative for the electrochemical study of metal complexation by thiol-containing peptides

Abstract Constant current chronopotentiometric stripping analysis using adsorptive accumulation and negative current (AdSCP) was applied as an alternative for the study of metal complexation of glutathione (GSH) or (γ-Glu-Cys)2-Gly (PC2) with zinc ions on hanging mercury drop electrode. The behavior of the formed Zn-complexes was studied using voltammetric and chronopotentiometric methods. A multivariate curve resolution method by alternating least-squares (MCR-ALS) applied to DP voltammetric and chronopotentiometric measurements of Zn–PC2 system made possible the formulation of a complexation model. Moreover, the use of small currents in AdSCP allows one to obtain acceptable sensitivities and signal separation at very low concentrations, which is important in peptide studies under conditions similar to these of natural media.

Constant Current Stripping Chronopotentiometry for the Study of Adsorbing Inert and Electrochemically Nonreversible Metal Complexes at Low Concentrations: Application to Cd and Zn Metallothioneins

Constant current chronopotentiometric stripping analysis using adsorptive accumulation and negative stripping current (AdSCP) was applied for the study of behavior of rabbit liver Cd-Zn and Zn metallothionein (Cd-Zn-MT, ZnMT) on hanging mercury drop electrode. Electrochemically inert or labile behavior of complexes can be distinguished with the application of high (1000 nA) or low (100 to 20 nA) current. Using high current, no influence of added Cd2+ or Zn2+ ions on the reduction of Cd(II) or Zn(II) complexed within MT molecule was observed, except of additions of Cd2+ to ZnMT, where bound Zn(II) was substituted by cadmium ions. With lowering of stripping current and increasing concentration of added Cd2+ or Zn2+ ions in solution progressive formation of reorganized complex with labile behavior is observed. Parallel measurement using DC voltammetry with different rates of polarization or differential pulse voltammetry were in agreement with AdSCP measurement. However, only chronopotentiometric method combines good sensitivity and signal separation at μM concentrations, inevitable in MT studies.

Comparison of constant-current stripping chronopotentiometry and anodic stripping voltammetry in metal speciation studies using mercury drop and film electrodes

Capabilities for heavy metal speciation of anodic stripping voltammetry (ASV) and constant-current stripping chronopotentiometry (SCP) in both mercury drop (HMDE) and mercury film rotating disk (MFE-RDE) electrodes are compared. For this purpose, the Cd(II)–glycine and Cd(II)–polymethacrylate (PMA) systems are used as models of simple labile and macromolecular labile complexes adsorbing onto the electrode, respectively. The results suggest that SCP could be a valuable alternative to the more widespread ASV in this kind of study. Concerning the electrode, the MFE-RDE is less user-friendly than the HMDE, but presents a better definition of both the hydrodynamic conditions during the deposition step and the stripping regime during the oxidation. An important interference in SCP is the dissolved oxygen, which can be minimised by combining relatively large oxidation currents and low stirring rates. Moreover, for Cd–PMA, double peaks have been observed in both ASV and SCP, which seems to be due to the lack of enough ligand excess to complex the metal ions released by the amalgam oxidation. Anyway, this problem can be minimised by optimising the rotation rate of the electrode and ensuring enough ligand excess.

Stripping chronopotentiometric detection of copper using screen-printed three-electrode system—application to acetic-acid bioavailable fraction from soil samples

Single-use sensors, incorporating a three-electrode configuration (graphite carbon-working electrode; carbon-counter electrode and silver/silver chloride-reference electrode), have been fabricated on a polyester substrate using low cost screen-printing (thick-film) technology. These electrodes coupled with constant current stripping chronopotentiometry (CCSCP), has provided a convenient screening tool for on-site detection of trace levels of copper. Modification of the graphite carbon surface based on in situ deposition of mercury film has been carried out. By appropriate choice of supporting medium and applied constant stripping current, well-resolved and reproducible response for copper was obtained. The stripping response for copper following 2 min deposition was linear over the concentration range examined (10–2000 ppb) with detection limit of 6 ppb using 2 M hydrochloric acid (HCl). Successful applications of the sensing device to acetic-acid bioavailable fraction of a certified reference material (CRM 601, a lake sediment) and soil samples are demonstrated.

Determination of metallothionein at the femtomole level by constant current stripping chronopotentiometry.

Metallothionein (MT) from rabbit liver was analyzed by differential pulse polarography, cyclic voltammetry, square wave voltammetry, and chronopotentiometric stripping analysis (CPSA) with a hanging mercury drop electrode under various conditions. The highest sensitivity of the MT determination was obtained with CPSA which produced a well-developed peak H due to catalytic hydrogen evolution at highly negative potentials. The highest peak H was obtained in borate buffer close to pH 8.0. In this medium, subnanomolar concentrations of MT were detectable. In the adsorptive transfer stripping (medium exchange) experiments, determination of few femtomoles of MT in 5-microL aliquots of the analyte was possible. CPSA determination of MT in various tissues of carp (Cyprinus carpio) yielded values in agreement with the published data.

Stripping analysis of nucleic acids at a heated carbon paste electrode.

A new electrically heated carbon paste electrode has been developed for performing adsorptive stripping measurements of trace nucleic acids. Such coupling of electrochemistry at electrically heated electrodes with adsorptive constant-current stripping chronopotentiometry offers distinct advantages for trace measurements of nucleic acids. The application of increased temperatures during the deposition step results in dramatic (4-34-fold, depending on temperature applied) enhancement of the stripping signal. Such improvement is attributed to the accumulation step at the heated electrode. Forced thermal convection near the electrode surface facilitates the use of quiescent solutions and hence of ultrasmall volumes. Using an electrode temperature of 32 degrees C and a quiescent solution during the 1-min accumulation, the response is linear over the 1-8 mg/L range tested, with a detection limit of 0.5 mg/L. Such electrode heating technology offers great promise for various applications involving thermal manipulations of nucleic acids.

Calibrationless determination of mercury by flow-through stripping coulometry.

Trace concentrations of Hg were determined in a flow-system by constant current stripping chronopotentiometry in coulometric mode. Mercury was electrodeposited from the flowing sample solution in an electrochemical flow-through cell on a large surface porous electrode plated with a thin layer of gold. The deposited mercury was then stripped with constant current and the potential change of the working electrode was recorded and evaluated. Since complete electrochemical yields were achieved at both the deposition and dissolution steps, the mercury concentration in the sample solution could be calculated from Faraday's law. The detection limit and reproducibility of the method were about 0.1 ng/ml for 10 ml sample solution and 4%, respectively. The time for a complete analysis was 2 to 5 min. The utility of the method was demonstrated with the analysis of reference materials, water samples, waste materials, plants and charcoal catalysts.